1. Field of the Invention
The present invention relates to a multi-layer phase retarder with the retardation in the front and perspective directions, and the wavelength dispersion thereof controlled, capable of providing a liquid crystal display device, or the like, with the excellent display quality in a wide viewing angle range.
The present application is based on Japanese Patent Application No. Hei. 11-331203, which is incorporated herein by reference.
2. Description of the Related Art
A retardation capable of providing a liquid crystal display device with the excellent display quality in a wide viewing angle range by preferably compensating the retardation by a birefringence of a liquid crystal cell in a wide range in the front and perspective directions is called for. However, according to a conventional single layer phase retarder made of a uni-axial or bi-axial stretched film, even if the retardation in the front and perspective directions can be compensated, a problem is involved in that the wavelength dispersion of the retardation can hardly be compensated. The wavelength dispersion appears as the coloring problem in the black and white display.
An object of the invention is to provide a phase retarder capable of controlling the wavelength dispersion as well as the retardation in the front and perspective directions so as to provide a liquid crystal display device with the excellent display quality by preventing coloring of the white and black display, or the like in a wide viewing angle range.
The invention provides a multi-layer phase retarder comprising a laminated member of a phase retarder satisfying 1.05xe2x89xa6xcex1 less than 1.3 and xcex2xe2x89xa61, and a phase retarder satisfying 1 less than xcex1 less than 1.05 and xcex2 greater than 1 with the following proviso. The retardation in the normal direction by a light beam of a 400 nm wavelength is R1, the retardation in the normal direction by a light beam of a 550 nm is R2, the retardation in the perpendicular direction in the state tilted by 40 degrees with respect to the normal direction with the slow axis as the rotation axis is R3, and R1/R2 is xcex1 and R3/R2 is xcex2. An elliptical polarizer is a laminated member of the multi-layer phase retarder, and a polarizer. A liquid crystal display device includes the multi-layer phase retarder, or the same and a polarizer at least on one side of a liquid crystal cell.
According to the invention, since the laminated member comprises a combination of phase retarders satisfying the xcex1 and xcex2, in addition to the retardation in the front and perspective directions, the wavelength dispersion thereof can also be controlled so that a phase retarder capable of providing a liquid crystal display device with the excellent display quality can be obtained by preventing coloring of the black and white display, or the like by compensating the retardation of a liquid crystal cell and the wavelength dispersion thereof in a wide front and perspective viewing angle range.
That is, the retardation is defined by the multiple (xcex94nd) of the refractive index difference (xcex94n) of the double refraction lights and the optical path length (d) Since the above-mentioned xcex1 denotes the wavelength dispersion characteristics of the retardation in the normal direction and the xcex2 denotes the angle dependency characteristics of the retardation, by providing the phase retarders with a combination of 1.05xe2x89xa6xcex1 less than 1.3 and 1 less than xcex1xcex1 less than 1.05, and a combination of xcex2xe2x89xa61 and xcex2 greater than 1, the retardation of each phase retarder and the wavelength dispersion by its xcex1 characteristics can be adjusted as well as the angle dependency of the retardation by the xcex2 characteristics can be adjusted by controlling the crossing angle of these optical axes in an appropriate condition such as parallel and orthogonal so that the retardation in the front and perspective directions and the wavelength dispersion thereof can be controlled. Since the wavelength dispersion is an attribute of the polymer comprising the single layer phase retarder in the case of a single layer phase retarder, it is difficult to control the wavelength dispersion therein.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.